Methods for linewidth modification and apparatus implementing the same

ABSTRACT

A linear-shaped core structure of a first material is formed on an underlying material. A layer of a second material is conformally deposited over the linear-shaped core structure and exposed portions of the underlying material. The layer of the second material is etched so as to leave a filament of the second material on each sidewall of the linear-shaped core structure, and so as to remove the second material from the underlying material. The linear-shaped core structure of the first material is removed so as to leave each filament of the second material on the underlying material. Each filament of the second material provides a mask for etching the underlying material. Each filament of the second material can be selectively etched further to adjust its size, and to correspondingly adjust a size of a feature to be formed in the underlying material.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/413,284, filed Nov. 12, 2010, entitled “Methods for Linewidth Modification and Apparatus Implementing the Same,” the disclosure of which is incorporated herein by reference in its entirety. Per 35 U.S.C. 119(e)(3), because the day that is 12 months after the filing date of U.S. Provisional Patent Application No. 61/413,284, falls on a Saturday, the period of pendency of U.S. Provisional Patent Application No. 61/413,284, is extended to the next succeeding business day of Monday, Nov. 14, 2011.

BACKGROUND

A push for higher performance and smaller die size drives the semiconductor industry to reduce circuit chip area by approximately 50% every two years. The chip area reduction provides an economic benefit for migrating to newer technologies. The 50% chip area reduction is achieved by reducing the feature sizes between 25% and 30%. The reduction in feature size is enabled by improvements in manufacturing equipment and materials. For example, improvement in the lithographic process has enabled smaller feature sizes to be achieved, while improvement in chemical mechanical polishing (CMP) has in-part enabled a higher number of interconnect layers.

In the evolution of lithography, as the minimum feature size approached the wavelength of the light source used to expose the feature shapes, unintended interactions occurred between neighboring features. Today minimum feature sizes are being reduced below 45 nm (nanometers), while the wavelength of the light source used in the photolithography process remains at 193 nm. The difference between the minimum feature size and the wavelength of light used in the photolithography process is defined as the lithographic gap. As the lithographic gap grows, the resolution capability of the lithographic process decreases.

An interference pattern occurs as each shape on the mask interacts with the light. The interference patterns from neighboring shapes can create constructive or destructive interference. In the case of constructive interference, unwanted shapes may be inadvertently created. In the case of destructive interference, desired shapes may be inadvertently removed. In either case, a particular shape is printed in a different manner than intended, possibly causing a device failure. Correction methodologies, such as optical proximity correction (OPC), attempt to predict the impact from neighboring shapes and modify the mask such that the printed shape is fabricated as desired. The quality of the light interaction prediction is declining as process geometries shrink and as the light interactions become more complex.

In view of the foregoing, solutions are sought for improvements in integrated circuit design, layout, and fabrication that can improve management of lithographic gap issues as technology continues to progress toward smaller semiconductor device feature sizes.

SUMMARY

In one embodiment, a method is disclosed for fabricating a mask for etching of linear-shaped structures for an integrated circuit. The method includes forming a plurality of linear-shaped core structures of a first material on an underlying material. The method also includes conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the underlying material. The method also includes etching the layer of the second material so as to leave a filament of the second material on each sidewall of each of the linear-shaped core structures, and so as to remove the second material from the underlying material. The method also includes depositing a third material over each filament of the second material. The method also includes removing a portion of the third material to as to expose one or more of the filaments of the second material. The method also includes etching the exposed filaments of the second material so as to leave thinner filaments of the second material. The method also includes removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the underlying material, whereby the filaments of the second material provides a mask for etching the underlying material.

In one embodiment, a method is disclosed for fabricating linear-shaped conductive structures for an integrated circuit. The method includes depositing a layer of a conductive material over a substrate. The method also includes forming a plurality of linear-shaped core structures of a first material on the conductive material. The method also includes conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the conductive material. The method also includes etching the layer of the second material so as to leave a filament of the second material on each sidewall of each of the linear-shaped core structures and so as to remove the second material from the conductive material. The method also includes depositing a third material over each filament of the second material. The method also includes removing a portion of the third material to as to expose one or more of the filaments of the second material. The method also includes etching the exposed filaments of the second material so as to leave thinner filaments of the second material. The method also includes removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the conductive material, whereby the filaments of the second material provide a mask for etching the conductive material. The method also includes etching the conductive material so as to leave linear-shaped portions of the conductive material beneath the filaments of the second material. The method also includes removing the filaments of the second material from the linear-shaped portions of the conductive material.

Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of the gate electrode layer of an example logic circuit with uniform conductive segment line-widths, in accordance with an example embodiment.

FIG. 2 shows a plan view of the gate electrode layer of an example logic circuit with two different conductive segment line-widths, and with conductive segment line-widths grouped for the same optical resolution as a core pattern, in accordance with an example embodiment.

FIG. 3 shows a plan view of the gate electrode layer of an example logic circuit with two different conductive segment line-widths, and with line-widths patterned with a resolution higher than used for the core pattern, in accordance with an example embodiment.

FIG. 4 shows a plan view of the gate electrode layer of an example logic circuit with three different conductive segment line-widths, and with line-widths grouped for the same optical resolution as a core pattern, in accordance with an example embodiment.

FIG. 5A shows a plan view, i.e., top view, of a core pattern for use in forming a gate electrode layer of an example logic circuit, in accordance with an example embodiment.

FIG. 5B shows the plan view of the core pattern of FIG. 5A following dielectric deposition and etching processes to form sidewall filaments 531, 533, and 535, in accordance with an example embodiment.

FIG. 5C shows the plan view of the sidewall filaments 531, 533, 535 of FIG. 5B after the core pattern, including core structures 521, 523, and 525, has been removed, in accordance with an example embodiment.

FIG. 5D shows a plan view of a cut pattern overlying the sidewall filaments 531, 533, 535 of FIG. 5C, prior to etching the sidewall filaments 531, 533, 535 in the cut pattern areas 541, 543, 545, and 547, in accordance with an example embodiment.

FIG. 5E shows the plan view of the sidewall filaments 531, 533, 535 of FIG. 5D after they have been etched within the cut pattern areas 541, 543, 545, and 547 as shown in FIG. 5D, in accordance with an example embodiment.

FIG. 6A shows a plan view, i.e., top view, of a core pattern that includes core structures 621, 623, and 625, surrounded by sidewall filaments 631, 633, and 635, respectively, in accordance with an example embodiment.

FIG. 6B shows the plan view of FIG. 6A after the etching process to reduce the width of the sidewall filament 633 that is exposed through the mask opening 641, in accordance with an example embodiment.

FIG. 6C shows the plan view of FIG. 6B after the first etching process to reduce the width of the sidewall filament 633, in accordance with an example embodiment.

FIG. 6D shows the plan view of FIG. 6C after the second etching process to reduce the width of the sidewall filament 631, in accordance with an example embodiment.

FIG. 7A shows vertical cross-section view of a core pattern for use in forming a gate electrode layer of an example logic circuit, in accordance with an example embodiment.

FIG. 7B shows the cross-section view of FIG. 7A, after deposition of a material layer 721 which will later become sidewall filaments, in accordance with an example embodiment.

FIG. 7C shows the cross-section view of FIG. 7B, after the material layer 721 has been etched to transform it into sidewall filaments 731, 732, 733, 734, 735, 736 formed along sides of the core structures 711, 713, 715, in accordance with an example embodiment.

FIG. 7D shows the cross-section view of FIG. 7C with a mask material 706 deposited to cover the core structures 711, 715, and their sidewall filaments 731, 732, 735, 736, and leave the core structure 713 and its sidewall filaments 733, 734 exposed, in accordance with an example embodiment.

FIG. 7E shows the cross-section view of FIG. 7C, after the sidewall filaments 733 and 734 have been selectively etched to reduce their width sizes, in accordance with an example embodiment.

FIG. 7F shows the cross-section view of FIG. 7E with a mask material 706 deposited to cover the core structures 713, 715, and their sidewall filaments 733, 734, 735, 736, and leave the core structure 711 and its sidewall filaments 731, 732 exposed, in accordance with an example embodiment.

FIG. 7G shows the cross-section view of FIG. 7E, after the sidewall filaments 731 and 732 have been selectively etched to reduce their width sizes, in accordance with an example embodiment.

FIG. 7H shows the cross-section view of FIG. 7G, after the core structures 711, 713, 715 have been removed, in accordance with an example embodiment.

FIG. 7I hows the cross-section view of FIG. 7H, after the underlying gate conductor material layer 705 has been etched in regions between the sidewall filaments 731, 732, 733, 734, 735, 736, in accordance with an example embodiment.

FIG. 7J shows the cross-section view of FIG. 7I, after the sidewall filaments 731, 732, 733, 734, 735, 736 have been removed, thereby leaving the etched gate conductor material layer 705, in accordance with an example embodiment.

FIG. 8A shows a vertical cross-section view of a core structure 803 formed on a conductive material layer 801 (e.g., gate conductor material layer 801), in accordance with an example embodiment.

FIG. 8B shows the cross-section view of FIG. 8A, after an etching process which leaves a full-width sidewall filament 850, in accordance with an example embodiment.

FIG. 8C shows the cross-section view of FIG. 8B, after the core structure 803 has been removed, and the sidewall filaments 850 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment.

FIG. 8D shows the cross-section of FIG. 8B following a further etching process to obtain sidewall filaments 853 of reduced width 873, relative to the sidewall filaments 850 of FIG. 8B, in accordance with an example embodiment.

FIG. 8E shows the cross-section view of FIG. 8D, after the core structure 803 and outside sidewall filament layer 815 have been removed, and the sidewall filaments 853 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment.

FIG. 8F shows the cross-section of FIG. 8D following a further etching process to reduce the sidewall filament 855 width 875 to essentially the thickness of the first deposited sidewall filament material layer 811, in accordance with an example embodiment.

FIG. 8G shows the cross-section view of FIG. 8F, after the core structure 803 and sidewall filament layer 813 have been removed, and the sidewall filaments 855 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment.

FIG. 9A shows a vertical cross-section view of a core structure 903 formed on a conductive material layer 901 (e.g., gate conductor material layer 901), in accordance with an example embodiment.

FIG. 9B shows the cross-section view of FIG. 9A, after an etching process which leaves sidewall filaments 911 and 912 of width size 950, in accordance with an example embodiment.

FIG. 9C shows the cross-section view of FIG. 9B, after the core structure 903 has been removed, and the sidewall filaments 911, 912 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

FIG. 9D shows the cross-section of FIG. 9B, after further etching of the sidewall filaments 911 and 912 to obtain sidewall filaments 921 and 922 of reduced width size 953, in accordance with an example embodiment.

FIG. 9E shows the cross-section view of FIG. 9D, after the core structure 903 has been removed, and the sidewall filaments 921, 922 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

FIG. 9F shows the cross-section of FIG. 9D, after further etching of the sidewall filaments 921 and 922 to obtain sidewall filaments 931 and 932 of even further reduced width size 955, in accordance with an example embodiment.

FIG. 9G shows the cross-section view of FIG. 9F, after the core structure 903 has been removed, and the sidewall filaments 931, 932 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

FIG. 10 shows a plan view of the gate electrode layer of a portion of an example SRAM cell with gate electrode layer conductive segments (1001, 1003, 1005, 1007, 1009, 1011, 1013, 1015) of uniform width size, as measured in the direction (x), in accordance with an example embodiment.

FIG. 11 shows a plan view of the gate electrode layer of a portion of an example SRAM cell with gate electrode layer conductive segments (1101, 1103, 1105, 1107, 1109, 1111, 1113, 1115) of non-uniform width size, as measured in the direction (x), in accordance with an example embodiment.

FIG. 12 shows a flowchart of a method for fabricating a mask for etching of linear-shaped structures for an integrated circuit, in accordance with one embodiment of the present invention.

FIG. 13 shows a flowchart of a method for fabricating a mask for etching of linear-shaped structures for an integrated circuit, in accordance with one embodiment of the present invention.

FIG. 14 shows a flowchart of a method for fabricating linear-shaped conductive structures for an integrated circuit, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Integrated circuit scaling has been enabled to a large extent by improvements in photolithography equipment resolution and overlay. The resolution capability was such that random logical functions could be drawn with two-dimensional (2D) bent layout shapes with few restrictions on layout shape dimensions or relationships between layout shapes. Some parts of certain types of integrated circuits (IC's), for example memory cells in a DRAM or Flash memory, were drawn with more regular layout patterns to permit reducing the feature sizes and hence the memory bit size.

As optical lithography has reached a cost-driven limit of the 193 nm ArF excimer laser light source and a lens numerical aperture of 0.93 (or 1.35 for water immersion systems), other approaches are being considered. One such approach is double patterning, in which the layout pattern is split into two parts, each of which can be separately processed with optical lithography equipment.

One approach to double patterning for regular layout patterns is SDP (spacer double patterning). This approach uses the following sequence to reduce the layout pattern shape-to-shape pitch by a factor of two:

-   -   1. standard optical lithography to pattern a “core”     -   2. etch the core and remove the resist     -   3. deposit a different material which can be etched selectively         relative to the core     -   4. etch the deposited film, leaving sidewall material and the         core     -   5. etch the core, leaving only the sidewall material     -   6. cut the sidewall material to create separate parts     -   7. etch the underlying material using the sidewall material as         the mask     -   8. remove the sidewall material, leaving the underlying material         with the desired pattern.

One attribute of this approach is that all of the sidewall filaments are uniform in line-width. This is desirable for the gate electrode layer, since uniform MOS transistor lengths give uniform circuit speed and leakage.

However, there are cases in which different gate electrode line-widths are useful, such as in analog circuits, in SRAM bit cells, in IO (input/output) cells, and for power optimization using several gate electrode critical dimensions (CD's) or line-widths, by way of example. Therefore, it can be necessary to design circuits that have different gate line-widths and/or MOS transistor structures with different line-widths. Accordingly, methods are needed to design and manufacture these types of circuits. Embodiments of such methods are disclosed herein.

Although the exemplary descriptions herein are provided within the context of the gate electrode layer, the approaches and principles illustrated herein can be applied to any masking layer/device layer in which SDP is done. Also, in some cases, multiple applications of SDP can be performed to obtain a pitch division by 4 or more. The “core” as depicted in the figures herein can either be a directly patterned core, or a line coming from a first SDP sequence which is now used as the “core” for a second SDP sequence. The linewidth modifications could be applied either after the first sequence, the second sequence, or both.

Gate linewidth modification is an effective method to control MOS transistor “off” or “leakage” current since. At technology nodes roughly below 28 nm (nanometers), the gate electrode is not patterned directly from a mask pattern. Instead, because of photolithography limits on pitch and the need for reduced LER (line-edge-roughness), the fabrication is done with the SDP process sequence. A “mold” or “core” is patterned and etched, then a filament is created around the edge. The width of the filament is uniform, and becomes the linewidth of the gate electrode. Hence, the gate linewidths are the same within the tolerance of the filament process.

A chip design is proposed which uses multiple gate electrode line-widths. The line-width is chosen based on requirements such as:

-   -   1. Relative current at a given gate bias for analog circuits     -   2. Ratio of current for select and pull-down transistors in an         SRAM bit cell     -   3.Field-dependent breakdown voltage for IO transistors     -   4. Power optimized timing path, in which some transistors have         gate lengths adjusted to reduce speed and leakage current or to         increase speed and leakage current

Structures on the chip are proposed with different gate electrode line-widths. These structures can be applied to functions such as:

-   -   1. Analog circuits     -   2. SRAM bit cells     -   3. IO cells     -   4. Logic cells selected for power/speed optimization

Example methods to create the structures on the chip include:

-   -   1. Individually patterned lines with different widths     -   2. SDP pitch division flow to create lines, followed by circuit         customization with cuts         -   a. SDP to create uniform lines         -   b. SDP with different sidewall filaments created with             optical resolution or sub-optical resolution (e.g., e-beam)         -   c. SDP with multiple film depositions and patterned etches             to achieve different line-widths (combinations of etch             selectivity are required, but the CD is well controlled by             the film thicknesses)         -   d. SDP with patterned etches, each etch creating a different             line-width through etch time or etch rate or both

FIG. 1 shows a plan view of the gate electrode layer of an example logic circuit with uniform conductive segment line-widths, in accordance with an example embodiment. The conductive segments of uniform line-width are represented by shapes 101, 103, 105, 107, 109, 111, 113, and 115.

FIG. 2 shows a plan view of the gate electrode layer of an example logic circuit with two different conductive segment line-widths, and with conductive segment line-widths grouped for the same optical resolution as a core pattern, in accordance with an example embodiment. The conductive segments of a first larger line width are represented by shapes 201, 203, 209, 211, and 213. The conductive segments of a second smaller line width are represented by shapes 205, 207, and 215.

FIG. 3 shows a plan view of the gate electrode layer of an example logic circuit with two different conductive segment line-widths, and with line-widths patterned with a resolution higher than used for the core pattern, in accordance with an example embodiment. The conductive segments of a first larger line width are represented by shapes 301, 303, and 311. The conductive segments of a second smaller line width are represented by shapes 305, 307, 309, 313, and 315.

FIG. 4 shows a plan view of the gate electrode layer of an example logic circuit with three different conductive segment line-widths, and with line-widths grouped for the same optical resolution as a core pattern, in accordance with an example embodiment. The conductive segments of a first larger line width are represented by shapes 409 and 411. The conductive segments of a second smaller line width are represented by shapes 405, 407, and 415. The conductive segments of a third smallest line width are represented by shapes 401, 403, and 413.

FIG. 5A shows a plan view, i.e., top view, of a core pattern for use in forming a gate electrode layer of an example logic circuit, in accordance with an example embodiment. The core pattern includes core structures 521, 523, and 525. The core structures 521, 523, and 525 are temporary structures that are formed of a material that can be subsequently removed. For example, the core structures 521, 523, and 525 can be formed of photoresist material or advanced patterning film (APF), among other types of materials. The core pattern is formed above a conductive layer that is to be formed into conductive segments to create the gate electrode layer.

FIG. 5B shows the plan view of the core pattern of FIG. 5A following dielectric deposition and etching processes to form sidewall filaments 531, 533, and 535, in accordance with an example embodiment. The sidewall filaments are formed of a material that is suitable for use as a hard-mask material for subsequent etching of the underlying conductive layer that is to be formed into conductive segments to create the gate electrode layer.

FIG. 5C shows the plan view of the sidewall filaments 531, 533, 535 of FIG. 5B after the core pattern, including core structures 521, 523, and 525, has been removed, in accordance with an example embodiment.

FIG. 5D shows a plan view of a cut pattern overlying the sidewall filaments 531, 533, 535 of FIG. 5C, prior to etching the sidewall filaments 531, 533, 535 in the cut pattern areas 541, 543, 545, and 547, in accordance with an example embodiment.

FIG. 5E shows the plan view of the sidewall filaments 531, 533, 535 of FIG. 5D after they have been etched within the cut pattern areas 541, 543, 545, and 547 as shown in FIG. 5D, in accordance with an example embodiment. At this point, the sidewall filaments 531, 533, 535 form a patterned hard mask that can be used to etch the underlying conductive material layer to form conductive structures within a gate electrode layer of the example logic circuit.

FIG. 6A shows a plan view, i.e., top view, of a core pattern that includes core structures 621, 623, and 625, surrounded by sidewall filaments 631, 633, and 635, respectively, in accordance with an example embodiment. In one embodiment, the core pattern and surrounding sidewall filaments 631, 633, and 635 of FIG. 6A are formed as part of a hard mask creation process, wherein the hard mask is to be used for etching an underlying conductive layer of material to form conductive structures within a gate electrode layer of an integrated circuit device. As with the previous example of FIGS. 5A-5E, the sidewall filaments 631, 633, and 635 can be formed around the core structures 621, 623, and 625 by dielectric deposition and etching processes, by way of example. FIG. 6A also shows an opening 641 in a mask pattern that is deposited to overly the core structures 621, 623, 625, and sidewall filaments 631, 633, 635. In this example, the mask pattern covers core structures 621, 625 and their surrounding sidewall filaments 631 and 635. The opening 641 in the mask pattern exposes the sidewall filament 633 to an etching process. In this manner, the sidewall filament 633 can be etched to reduce its width, as measured outward from the core structure 623, without affecting the sizes of sidewall filaments 631 and 635. Therefore, sidewall filament 633 can be selectively adjusted in size, i.e., width.

FIG. 6B shows the plan view of FIG. 6A after the etching process to reduce the width of the sidewall filament 633 that is exposed through the mask opening 641, in accordance with an example embodiment.

FIG. 6C shows the plan view of FIG. 6B after the first etching process to reduce the width of the sidewall filament 633, in accordance with an example embodiment. FIG. 6C also shows the overlying mask pattern (that is deposited to overly the core structures 621, 623, 625, and sidewall filaments 631, 633, 635) adjusted to have an opening 643 which exposes the sidewall filament 631 without exposing the other sidewall filaments 633 and 635. With the sidewall filament 631 selectively exposed by way of the mask opening 643, the sidewall filament 631 can be etched to independently adjust its width size.

FIG. 6D shows the plan view of FIG. 6C after the second etching process to reduce the width of the sidewall filament 631, in accordance with an example embodiment. FIG. 6D also shows the core structures 621, 623, 625 removed. The sidewall filaments 631, 633, and 635 now have differing widths, and can be cut as needed, similar to the examples of FIGS. 5D-5E, to define a hard mask for etching of an underlying conductive material layer.

FIG. 7A shows vertical cross-section view of a core pattern for use in forming a gate electrode layer of an example logic circuit, in accordance with an example embodiment. The cross-section shows a substrate 701, a gate dielectric material layer 703 deposited on the substrate 701, and a gate conductor material layer 705 deposited on the gate dielectric material layer 703. The cross-section also shows core structures 711, 713, and 715 formed on the gate conductor material layer 705. It should be understood that the core structures 711, 713, and 715 are formed through a deposition, mask patterning, and etching process conducted above the gate conductor material layer 705.

FIG. 7B shows the cross-section view of FIG. 7A, after deposition of a material layer 721 which will later become sidewall filaments, in accordance with an example embodiment.

FIG. 7C shows the cross-section view of FIG. 7B, after the material layer 721 has been etched to transform it into sidewall filaments 731, 732, 733, 734, 735, 736 formed along sides of the core structures 711, 713, 715, in accordance with an example embodiment.

FIG. 7D shows the cross-section view of FIG. 7C with a mask material 706 deposited to cover the core structures 711, 715, and their sidewall filaments 731, 732, 735, 736, and leave the core structure 713 and its sidewall filaments 733, 734 exposed, in accordance with an example embodiment. The mask material 706 protects the core structures 711, 715, and their sidewall filaments 731, 732, 735, 736 from a subsequent etching process, and thereby enables further selective etching of the sidewall filaments 733, 734.

FIG. 7E shows the cross-section view of FIG. 7C, after the sidewall filaments 733 and 734 have been selectively etched to reduce their width sizes, in accordance with an example embodiment. As illustrated by the example in FIGS. 6A-6B, a mask layer can be formed with an opening defined to expose the core structure 713 and its surrounding sidewall filaments 733 and 734 to enable the selective etching, i.e., selective width size adjustment, of the sidewall filaments 733 and 734, relative to the other sidewall filaments 731, 732, 735, and 736.

FIG. 7F shows the cross-section view of FIG. 7E with a mask material 706 deposited to cover the core structures 713, 715, and their sidewall filaments 733, 734, 735, 736, and leave the core structure 711 and its sidewall filaments 731, 732 exposed, in accordance with an example embodiment. The mask material 706 protects the core structures 713, 715, and their sidewall filaments 733, 734, 735, 736 from a subsequent etching process, and thereby enables further selective etching of the sidewall filaments 731, 732.

FIG. 7G shows the cross-section view of FIG. 7E, after the surrounding sidewall filaments 731 and 732 have been selectively etched to reduce their width sizes, in accordance with an example embodiment. As illustrated by the example in FIGS. 6C-6D, a mask layer can be formed with an opening defined to expose the core structure 711 and its surrounding sidewall filaments 731 and 732 to enable the selective etching, i.e., selective width size adjustment, of the sidewall filaments 731 and 732, relative to the other sidewall filaments 733, 734, 735, and 736.

FIG. 7H shows the cross-section view of FIG. 7G, after the core structures 711, 713, 715 have been removed, in accordance with an example embodiment. The sidewall filaments 731, 732, 733, 734, 735, 736 provide a mask for etching the underlying gate conductor material layer 705. FIG. 7I shows the cross-section view of FIG. 7H, after the underlying gate conductor material layer 705 has been etched in regions between the sidewall filaments 731, 732, 733, 734, 735, 736, in accordance with an example embodiment. FIG. 7J shows the cross-section view of FIG. 7I, after the sidewall filaments 731, 732, 733, 734, 735, 736 have been removed, thereby leaving the etched gate conductor material layer 705, in accordance with an example embodiment.

FIG. 8A shows a vertical cross-section view of a core structure 803 formed on a conductive material layer 801 (e.g., gate conductor material layer 801), in accordance with an example embodiment. FIG. 8A also shows three different sidewall filament material layers 811, 813, and 815 sequentially and conformally deposited over the core structure 803 and surrounding/adjacent conductive material layer 801.

FIG. 8B shows the cross-section view of FIG. 8A, after an etching process which leaves a full-width sidewall filament 850, in accordance with an example embodiment. Considering that the sidewall filament 850 will serve as a hard mask to protect the underlying gate conductor material layer 801 during a subsequent etching process to form conductive segments within the gate electrode layer, and further considering that the core structure 803 will be removed prior to the subsequent etching process on the gate conductor material layer 801, the width size 870 of the sidewall filament 850 effectively defines the width size of the conductive segment to be formed within the gate conductor material layer 801. FIG. 8C shows the cross-section view of FIG. 8B, after the core structure 803 has been removed, and the sidewall filaments 850 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment.

Considering that the conductive segment formed within the gate conductor material layer 801 below the sidewall filament 850 is a gate electrode of a transistor, the width size 870 of the gate electrode of the transistor (which may also be referred to as the transistor's channel length) can be adjusted by adjusting the width size 870 of the sidewall filament. FIG. 8D shows the cross-section of FIG. 8B following a further etching process to obtain sidewall filaments 853 of reduced width 873, relative to the sidewall filaments 850 of FIG. 8B, in accordance with an example embodiment. It should be understood that the etching of the sidewall filaments can be controlled, by way of a mask pattern, such that either one or both of the sidewall filaments adjacent to the core structure 803 is etched, i.e., thinned. Also, it should be understood that the layered deposition of the sidewall filament material in the layers 811, 813, and 815 can provide control of sidewall filament etching, such that the etching will stop at the boundaries between the successively removed sidewall filament material layers.

FIG. 8E shows the cross-section view of FIG. 8D, after the core structure 803 and outside sidewall filament layer 815 have been removed, and the sidewall filaments 853 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment. FIG. 8F shows the cross-section of FIG. 8D following a further etching process to reduce the sidewall filament 855 width 875 to essentially the thickness of the first deposited sidewall filament material layer 811, in accordance with an example embodiment. FIG. 8G shows the cross-section view of FIG. 8F, after the core structure 803 and sidewall filament layer 813 have been removed, and the sidewall filaments 855 have been used as a mask for etching the underlying gate conductor material layer 801, in accordance with an example embodiment.

The examples of FIGS. 8A-8G utilized successively deposited sidewall filament material layers to provide a measure of etching control for the sidewall filaments, such that boundaries between the successively deposited sidewall filament material layers provided etching stops to facilitate sizing of the sidewall filaments, and correspondingly formed underlying gate electrode layer conductive structures. However, some etching processes may enable sidewall filament thickness control without requiring sidewall material layer boundaries.

For example, FIG. 9A shows a vertical cross-section view of a core structure 903 formed on a conductive material layer 901 (e.g., gate conductor material layer 901), in accordance with an example embodiment. FIG. 9A also shows a single sidewall filament material layer 911 conformally deposited over the core structure 903 and surrounding/adjacent conductive material layer 901.

FIG. 9B shows the cross-section view of FIG. 9A, after an etching process which leaves sidewall filaments 911 and 912 of width size 950, in accordance with an example embodiment. The width size 950 may represent a largest gate electrode layer conductive segment width size. In this case, the sidewall filaments 911 and 912 are ready to use as the hard mask for etching of the underlying gate conductor material layer 901. FIG. 9C shows the cross-section view of FIG. 9B, after the core structure 903 has been removed, and the sidewall filaments 911, 912 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

It may be necessary to form gate electrode layer conductive segments of reduced size. In this case, the etching of the sidewall filaments can continue until the desired width size is obtained. Again, it should be understood that appropriately formed mask patterns can expose any one or more sidewall filaments for etching and size adjustment. For example, FIG. 9D shows the cross-section of FIG. 9B, after further etching of the sidewall filaments 911 and 912 to obtain sidewall filaments 921 and 922 of reduced width size 953, in accordance with an example embodiment. FIG. 9E shows the cross-section view of FIG. 9D, after the core structure 903 has been removed, and the sidewall filaments 921, 922 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

Additionally, FIG. 9F shows the cross-section of FIG. 9D, after further etching of the sidewall filaments 921 and 922 to obtain sidewall filaments 931 and 932 of even further reduced width size 955, in accordance with an example embodiment. FIG. 9G shows the cross-section view of FIG. 9F, after the core structure 903 has been removed, and the sidewall filaments 931, 932 have been used as a mask for etching the underlying gate conductor material layer 901, in accordance with an example embodiment.

FIG. 10 shows a plan view of the gate electrode layer of a portion of an example SRAM cell with gate electrode layer conductive segments (1001, 1003, 1005, 1007, 1009, 1011, 1013, 1015) of uniform width size, as measured in the direction (x), in accordance with an example embodiment. Also, the example of FIG. 10 shows diffusion regions 1021 and 1023 of non-uniform size, i.e., of non-uniform active line-widths, to improve static noise margin. The principles disclosed herein with regard to FIGS. 1-9G can be used to form the gate electrode layer conductive segments (1001, 1003, 1005, 1007, 1009, 1011, 1013, 1015).

FIG. 11 shows a plan view of the gate electrode layer of a portion of an example SRAM cell with gate electrode layer conductive segments (1101, 1103, 1105, 1107, 1109, 1111, 1113, 1115) of non-uniform width size, as measured in the direction (x), in accordance with an example embodiment. Also, the example of FIG. 11 shows diffusion regions 1121 and 1123 of uniform size, i.e., of uniform active line-widths, to improve static noise margin. The principles disclosed herein with regard to FIGS. 1-9G can be used to form the gate electrode layer conductive segments (1101, 1103, 1105, 1107, 1109, 1111, 1113, 1115). This approach is suitable for FinFETs, in which the active regions, i.e., diffusion regions, are fins of uniform width.

The embodiments illustrated herein provide for patterning of the gate electrode layer, or for any layer that uses patterning that cannot be achieved by litho in a single step. Examples of other layers that may benefit from the embodiments shown herein can include metallization layers requiring multiple widths for power bussing etc. The patterning can be SDP patterning or litho-based double patterning. In one embodiment, the gate electrode layer (or other layer) line widths are selectively decreased by using a patterned trim step. In one embodiment, the gate electrode layer (or other layer) line widths are selectively increased by using a patterned resist reflow step. In one embodiment, the gate electrode layer (or other layer) patterning is completed by cutting the filaments based on a pattern set by the circuit layout.

FIG. 12 shows a flowchart of a method for fabricating a mask for etching of linear-shaped structures for an integrated circuit, in accordance with one embodiment of the present invention. The method includes an operation 1201 in which a linear-shaped core structure of a first material is formed on an underlying material. The method also includes an operation 1203 for conformally depositing a layer of a second material over the linear-shaped core structure and exposed portions of the underlying material. The method also includes an operation 1205 for etching the layer of the second material so as to leave a filament of the second material on each sidewall of the linear-shaped core structure, and so as to remove the second material from the underlying material. The method further includes an operation 1207 for removing the linear-shaped core structure of the first material so as to leave each filament of the second material on the underlying material, whereby each filament of the second material provides a mask for etching the underlying material.

In one embodiment, the linear-shaped core structure of the first material is formed on the underlying material in operation 1201 using a mask material patterned by an optical lithography process. Also, in this embodiment, the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process. In another embodiment, the linear-shaped core structure of the first material is formed on the underlying material in operation 1201 using a multiple mask patterning process, wherein each mask of the multiple mask patterning process is formed by an optical lithography process. Also, in this embodiment, the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.

In one embodiment, operation 1205 for etching the layer of the second material includes removing the second material from a top surface of the linear-shaped core structure of the first material so as to expose the top surface of the linear-shaped core structure of the first material. Also, in one embodiment, etching the layer of the second material in operation 1205 includes biasing an etching front in a direction toward the underlying material. It should be appreciated that the first material and the second material have different etching selectivities to enable removal of the first material without substantial removal of the second material during a given etching process.

In one embodiment, the method further includes an operation in which a cut mask is formed over the filaments of the second material so as to expose portions of the filaments of the second material for removal, so as to form ends of linear segments of the filaments of the second material. In this embodiment, the method correspondingly includes an operation for removing exposed portions of the filaments of the second material, whereby the linear segments of the filaments of the second material provide the mask for etching the underlying material.

FIG. 13 shows a flowchart of a method for fabricating a mask for etching of linear-shaped structures for an integrated circuit, in accordance with one embodiment of the present invention. The method includes an operation 1301 in which a plurality of linear-shaped core structures of a first material are formed on an underlying material. The method also includes an operation 1303 for conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the underlying material. An operation 1305 is then performed to etch the layer of the second material so as to leave a filament of the second material on each sidewall of each of the linear-shaped core structures and so as to remove the second material from the underlying material.

The method further includes an operation 1307 for depositing a third material over each filament of the second material. Then, in an operation 1309, a portion of the third material is removed so as to expose one or more filaments of the second material. The method continues with an operation 1311 for etching the exposed filaments of the second material so as to leave thinner filaments of the second material. The method also includes an operation 1313 for removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the underlying material, whereby the filaments of the second material provides a mask for etching the underlying material.

In one embodiment, each of the plurality of linear-shaped core structures of the first material is formed on the underlying material in operation 1301 using a mask material patterned by an optical lithography process. In this embodiment, the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process. In another embodiment, each of the plurality of linear-shaped core structures of the first material is formed on the underlying material in operation 1301 using a multiple mask patterning process. In this embodiment, each mask of the multiple mask patterning process is formed by an optical lithography process. Also, in this embodiment, the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.

It should be appreciated that the first material and the second material have different etching selectivities to enable removal of the first material without substantial removal of the second material during a given etching process. In one embodiment, etching the layer of the second material in operation 1305 includes removing the second material from a top surface of each of the plurality of linear-shaped core structures of the first material so as to expose the top surface of each of the plurality of linear-shaped core structures of the first material. In one embodiment, etching the layer of the second material in one or both of operations 1305 and 1311 can include biasing an etching front in a direction toward the underlying material.

In one embodiment, the method further includes an operation in which a cut mask is formed over the filaments of the second material so as to expose portions of the filaments of the second material for removal, so as to form ends of linear segments of the filaments of the second material. This embodiment also includes an operation for removing exposed portions of the filaments of the second material, whereby the linear segments of the filaments of the second material provide the mask for etching the underlying material.

In one embodiment, conformally depositing the layer of the second material over each of the linear-shaped core structures and exposed portions of the underlying material in operation 1303 includes conformally depositing multiple sub-layers of the second material. In this embodiment, each boundary between the multiple sub-layers of the second material provides an etch stop for a subsequent etching of the second material.

FIG. 14 shows a flowchart of a method for fabricating linear-shaped conductive structures for an integrated circuit, in accordance with one embodiment of the present invention. The method includes an operation 1401 for depositing a layer of a conductive material over a substrate. The method also includes an operation 1403 in which a plurality of linear-shaped core structures of a first material are formed on the conductive material. The method also includes an operation 1405 for conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the conductive material. The method also includes an operation 1407 for etching the layer of the second material so as to leave a filament of the second material on each sidewall of each of the linear-shaped core structures and so as to remove the second material from the conductive material. The method also includes an operation 1409 for depositing a third material over each filament of the second material. The method also includes an operation 1411 for removing a portion of the third material to as to expose one or more of the filaments of the second material. The method also includes an operation 1413 for etching the exposed filaments of the second material so as to leave thinner filaments of the second material. The method also includes an operation 1415 for removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the conductive material, whereby the filaments of the second material provide a mask for etching the conductive material. The method also includes an operation 1417 for etching the conductive material so as to leave linear-shaped portions of the conductive material beneath the filaments of the second material. The method also includes an operation 1419 for removing the filaments of the second material from the linear-shaped portions of the conductive material.

In one embodiment, the linear-shaped core structure of the first material is formed on the conductive material in operation 1403 using an optical lithography process. In this embodiment, the filaments of the second material on the conductive material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.

It should be appreciated that the first material and the second material have different etching selectivities to enable removal of the first material without substantial removal of the second material during a given etching process. Also, in one embodiment, etching the layer of the second material in operation 1407 includes biasing an etching front in a direction toward the conductive material.

In one embodiment, the method also includes an operation in which a cut mask is formed over the filaments of the second material so as to expose portions of the filaments of the second material for removal, so as to form ends of linear segments of the filaments of the second material. Also, in this embodiment, an operation is performed to remove exposed portions of the filaments of the second material, whereby the linear segments of the filaments of the second material provide the mask for etching the conductive material.

It should be understood that the methods disclosed herein can be used to create sidewall filaments having a thickness of less than or equal to 30 nanometers (nm), in various embodiments. Because the sidewall filaments provide a mask for fabricating underlying structures, it should be understood that the thickness of the sidewall filaments as measured horizontal to the substrate determines the size, e.g., critical dimension, of the underlying structures. For a 32 nm process node, the minimum as-drawn structure size is about 30 nm, which can be incremented by about 10% to obtain structure sizes of about 34 nm, 38 nm, etc. Also, with a 90% scaling process, the 30 nm minimum as-drawn structure size can be decreased to obtain about a 28 nm structure size. Therefore, at the 32 nm process node with the 90% scaling process applied, sidewall filaments can be formed to fabricate structure sizes of 28 nm, 32 nm, 36 nm, etc. For a 22 nm process node, the minimum as-drawn structure size is about 20 nm, which can be incremented by about 10% to obtain structure sizes of about 22 nm, 24 nm, etc. Also, with a 90% scaling process, the 20 nm minimum as-drawn structure size can be decreased to obtain about a 18 nm structure size. Therefore, at the 22 nm process node with the 90% scaling process applied, sidewall filaments can be formed to fabricate structure sizes of 18 nm, 20 nm, 22 nm, etc. For a 16 nm process node, the minimum as-drawn structure size is about 14 nm, which can be incremented by about 10% to obtain structure sizes of about 16 nm, 18 nm, etc. Also, with a 90% scaling process, the 14 nm minimum as-drawn structure size can be decreased to obtain about a 12 nm structure size. Therefore, at the 16 nm process node with the 90% scaling process applied, sidewall filaments can be formed to fabricate structure sizes of 12 nm, 14 nm, 16 nm, etc. It should be appreciated that structure size fabrication capabilities of future process nodes can be scaled by a factor of about 0.7 to about 0.8.

It should be understood that layout features associated with the methods disclosed herein can be implemented in a layout that is stored in a tangible form, such as in a digital format on a computer readable medium. For example, the layouts incorporating the layout features associated with the methods disclosed herein can be stored in a layout data file of one or more cells, selectable from one or more libraries of cells. The layout data file can be formatted as a GDS II (Graphic Data System) database file, an OASIS (Open Artwork System Interchange Standard) database file, or any other type of data file format suitable for storing and communicating semiconductor device layouts. Also, multi-level layouts including the layout features associated with the methods disclosed herein can be included within a multi-level layout of a larger semiconductor device. The multi-level layout of the larger semiconductor device can also be stored in the form of a layout data file, such as those identified above.

Also, the invention described herein can be embodied as computer readable code on a computer readable medium. For example, the computer readable code can include the layout data file within which one or more layouts including layout features associated with the methods disclosed herein are stored. The computer readable code can also include program instructions for selecting one or more layout libraries and/or cells that include a layout including layout features associated with the methods disclosed herein. The layout libraries and/or cells can also be stored in a digital format on a computer readable medium.

The computer readable medium mentioned herein is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network of coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Any of the operations described herein that form part of the invention are useful machine operations. The invention also relates to a device or an apparatus for performing these operations. The apparatus may be specially constructed for the required purpose, such as a special purpose computer. When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. Alternatively, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network the data maybe processed by other computers on the network, e.g., a cloud of computing resources.

The embodiments of the present invention can also be defined as a machine that transforms data from one state to another state. The data may represent an article, that can be represented as an electronic signal and electronically manipulate data. The transformed data can, in some cases, be visually depicted on a display, representing the physical object that results from the transformation of data. The transformed data can be saved to storage generally, or in particular formats that enable the construction or depiction of a physical and tangible object. In some embodiments, the manipulation can be performed by a processor. In such an example, the processor thus transforms the data from one thing to another. Still further, the methods can be processed by one or more machines or processors that can be connected over a network. Each machine can transform data from one state or thing to another, and can also process data, save data to storage, transmit data over a network, display the result, or communicate the result to another machine.

It should be further understood that the layout features associated with the methods disclosed herein can be manufactured as part of a semiconductor device or chip. In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on a semiconductor wafer. The wafer includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials.

While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention. 

What is claimed is:
 1. A method for fabricating a mask for etching of linear-shaped structures for an integrated circuit, comprising: forming a plurality of linear-shaped core structures of a first material on an underlying material, the plurality of linear-shaped core structures formed to extend lengthwise in a parallel manner so as to have commonly oriented lengthwise sidewalls; after forming the plurality of linear-shaped core structures of the first material, conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the underlying material; after conformally depositing the layer of the second material, etching the layer of the second material so as to leave a filament of the second material on each lengthwise sidewall of each of the linear-shaped core structures and so as to remove the second material from the underlying material; after etching the layer of the second material, depositing a third material over each filament of the second material; after depositing the third material, removing a portion of the third material so as to expose an entirety of at least one of the plurality of linear-shaped core structures of the first material and an entirety of each of the filaments of the second material present along each of its lengthwise sidewalls; after removing the portion of the third material, etching the exposed filaments of the second material so as to leave thinner filaments of the second material as measured in a direction perpendicular to the lengthwise sidewalls of the plurality of linear-shaped core structures; and after etching the exposed filaments of the second material so as to leave thinner filaments of the second material, removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the underlying material, whereby the filaments of the second material provides a mask for etching the underlying material.
 2. The method as recited in claim 1, wherein each of the plurality of linear-shaped core structures of the first material is formed on the underlying material using an optical lithography process, and wherein the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.
 3. The method as recited in claim 1, wherein each of the plurality of linear-shaped core structures of the first material is formed on the underlying material using a multiple mask patterning process, wherein each mask of the multiple mask patterning process is formed by an optical lithography process, and wherein the filaments of the second material on the underlying material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.
 4. The method as recited in claim 1, wherein etching the layer of the second material includes removing the second material from a top surface of each of the plurality of linear-shaped core structures of the first material so as to expose the top surface of each of the plurality of linear-shaped core structures of the first material.
 5. The method as recited in claim 1, wherein the first material and the second material have different etching selectivities to enable removal of the first material without substantial removal of the second material during a given etching process.
 6. The method as recited in claim 1, wherein etching the layer of the second material includes biasing an etching front in a direction toward the underlying material.
 7. The method as recited in claim 1, further comprising: forming a cut mask over the filaments of the second material so as to expose portions of the filaments of the second material for removal so as to form ends of linear segments of the filaments of the second material; and removing exposed portions of the filaments of the second material, whereby the linear segments of the filaments of the second material provide the mask for etching the underlying material.
 8. The method as recited in claim 1, wherein conformally depositing the layer of the second material over each of the linear-shaped core structures and exposed portions of the underlying material includes conformally depositing multiple sub-layers of the second material, wherein each boundary between the multiple sub-layers of the second material provides an etch stop for a subsequent etching of the second material.
 9. A method for fabricating linear-shaped conductive structures for an integrated circuit, comprising: depositing a layer of a conductive material over a substrate; after depositing the layer of the conductive material, forming a plurality of linear-shaped core structures of a first material on the conductive material, the plurality of linear-shaped core structures formed to extend lengthwise in a parallel manner so as to have commonly oriented lengthwise sidewalls; after forming the plurality of linear-shaped core structures of the first material, conformally depositing a layer of a second material over each of the linear-shaped core structures and exposed portions of the conductive material; after conformally depositing the layer of the second material, etching the layer of the second material so as to leave a filament of the second material on each lengthwise sidewall of each of the linear-shaped core structures and so as to remove the second material from the conductive material; after etching the layer of the second material, depositing a third material over each filament of the second material; after depositing the third material, removing a portion of the third material so as to expose an entirety of at least one of the plurality of linear-shaped core structures of the first material and an entirety of each of the filaments of the second material present along each of its lengthwise sidewalls; after removing the portion of the third material, etching the exposed filaments of the second material so as to leave thinner filaments of the second material as measured in a direction perpendicular to the lengthwise sidewalls of the plurality of linear-shaped core structures; after etching the exposed filaments of the second material so as to leave thinner filaments of the second material, removing the third material and the plurality of linear-shaped core structures of the first material so as to leave the filaments of the second material on the conductive material, whereby the filaments of the second material provide a mask for etching the conductive material; after removing the third material and the plurality of linear-shaped core structures of the first material, etching the conductive material so as to leave linear-shaped portions of the conductive material beneath the filaments of the second material; and after etching the conductive material, removing the filaments of the second material from the linear-shaped portions of the conductive material.
 10. The method as recited in claim 9, wherein the linear-shaped core structure of the first material is formed on the conductive material using an optical lithography process, and wherein the filaments of the second material on the conductive material collectively have dimensions and spacings too small to be directly formed by the optical lithography process.
 11. The method as recited in claim 9, wherein the first material and the second material have different etching selectivities to enable removal of the first material without substantial removal of the second material during a given etching process.
 12. The method as recited in claim 9, wherein etching the layer of the second material includes biasing an etching front in a direction toward the conductive material.
 13. The method as recited in claim 9, further comprising: forming a cut mask over the filaments of the second material so as to expose portions of the filaments of the second material for removal so as to form ends of linear segments of the filaments of the second material; and removing exposed portions of the filaments of the second material, whereby the linear segments of the filaments of the second material provide the mask for etching the conductive material. 